U.S. patent number 6,527,804 [Application Number 09/857,659] was granted by the patent office on 2003-03-04 for intervertebral disk prosthesis.
This patent grant is currently assigned to DIMSO (Distribution Medicale du Sud-Quest). Invention is credited to Fabien Gauchet, Regis Le Couedic.
United States Patent |
6,527,804 |
Gauchet , et al. |
March 4, 2003 |
**Please see images for:
( Certificate of Correction ) ** |
Intervertebral disk prosthesis
Abstract
An intervertebral disc prosthesis comprising two plates and a
cushion interposed between the plates is contemplated. The cushion
includes a compressible body having two ends in contact with the
plates. At least one of the ends is freely displaceable relative to
the plate in a parallel direction. Thus, the prosthesis imitates
and approximates the mechanical properties of a healthy natural
intervertebral disc.
Inventors: |
Gauchet; Fabien (Route de
Rocquemont, FR), Le Couedic; Regis (Cestas,
FR) |
Assignee: |
DIMSO (Distribution Medicale du
Sud-Quest) (FR)
|
Family
ID: |
9533876 |
Appl.
No.: |
09/857,659 |
Filed: |
July 20, 2001 |
PCT
Filed: |
December 09, 1999 |
PCT No.: |
PCT/FR99/03072 |
PCT
Pub. No.: |
WO00/35384 |
PCT
Pub. Date: |
June 22, 2000 |
Foreign Application Priority Data
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Dec 11, 1998 [FR] |
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98 15671 |
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Current U.S.
Class: |
623/17.12;
623/17.15; 623/17.16 |
Current CPC
Class: |
A61F
2/442 (20130101); A61F 2/30742 (20130101); A61F
2002/30563 (20130101); A61F 2002/30578 (20130101); A61F
2002/30565 (20130101); A61F 2310/00023 (20130101); A61F
2002/443 (20130101); A61F 2002/30069 (20130101); A61F
2002/30584 (20130101); A61F 2002/30581 (20130101) |
Current International
Class: |
A61F
2/44 (20060101); A61F 002/44 () |
Field of
Search: |
;623/17.12,17.13,17.15,17.16,17.11 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2 263 842 |
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Jul 1974 |
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DE |
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3741493 |
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Jun 1989 |
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DE |
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9000094.3 |
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Mar 1991 |
|
DE |
|
0356112 |
|
Dec 1993 |
|
EP |
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2 723 841 |
|
Mar 1996 |
|
FR |
|
Other References
English Translation of French No. 2,723,841.* .
09/857,726 Gauchet Et Al. filed Jul. 20, 2001..
|
Primary Examiner: Smith; Jeffrey A.
Attorney, Agent or Firm: Lerner, David, Littenberg, Krumholz
& Mentlik, LLP
Claims
What is claimed is:
1. Intervertebral disc prosthesis, comprising: tow plates; and a
cushion interposed between the plates, the cushion comprising a
compressible body including a compressible fluid, wherein the fluid
extends around the periphery of the body.
2. Prosthesis according to claim 1, wherein the fluid comprises a
gas.
3. Prosthesis according to claim 1, wherein the cushion is arranged
such that a fluid pressure is applied directly to the plates.
4. Prosthesis according to claim 1, wherein the cushion exhibits a
hysteresis-shaped curve of mechanical reaction to a compression as
a function of a variation in a dimension of the cushion in the
direction of the compression.
5. Prosthesis according to claim 4, wherein the cushion reaction to
the compression is less for relatively low reaction values than for
relatively high reaction values.
6. Prosthesis according to claim 4 or 5, wherein the cushion
reaction to the compression diminishes more for relatively high
reaction values than for relatively low reaction values.
7. Prosthesis according to claim 4 or 5, wherein the cushion
reaction to the compression has higher values when the cushion
grows than when it diminishes.
8. Prosthesis according to claim 1, wherein the prosthesis is a
lumbar intervertebral disk prosthesis.
9. Intervertebral disc prosthesis, comprising: two plates; and a
cushion interposed between the plates, the cushion comprising a
compressible body and including a compressible fluid, wherein the
fluid has a pressure such that the fluid is more compressible than
the body.
10. Intervertebral disc prosthesis, comprising: two plates; and a
cushion interposed between the plates, the cushion comprising a
compressible body made from a viscoelastic material and including a
compressible fluid.
11. Prosthesis according to claim 10, wherein the viscoelastic
material is silicone.
12. Intervertebral disc prosthesis, comprising: two plates; and a
cushion interposed between the plates, wherein the cushion
comprises a compressible body and includes a compressible fluid,
and wherein the body has at least one end defining a contact zone
with one of the plates and the prosthesis is arranged such that the
contact zone has a surface area which increases whenever a
stressing of the plates in the direction of the body is
increased.
13. Prosthesis according to claim 12, wherein the contact zone is
defined by a face of the plate and an end face of the body, one of
the faces being curved and convex and the other face being
flat.
14. Prosthesis according to claim 13, wherein the end face of the
body is curved and convex and the face of the plate is flat.
15. Prosthesis according to claim 12, wherein the contact zone is
defined by a face of the plate and an end face of the body, the
plate face and the body face being curved in at least one common
direction and being concave and convex, the concave face having at
least one radius of curvature greater than a corresponding radius
of curvature of the convex face.
16. Intervertebral disc prosthesis, comprising: two plates; and a
cushion interposed between the plates, wherein the cushion
comprises a compressible body and includes a compressible fluid,
and wherein the body has at least one end in contact with one of
the plates, the at least one end being free to move relative to the
plate in a direction parallel to the plate.
17. Prosthesis according to claim 16, wherein the end is
accommodated in a recess of the plate forming a lateral abutment
for the body.
18. Intervertebral disc prosthesis, comprising: two plates; and a
cushion interposed between the plates, wherein the cushion
comprises a compressible chamber containing a compressible fluid
such that the chamber has a cross-sectional area parallel to the
plates which is essentially invariable when variation occurs in a
compression of the cushion between the plates.
19. Intervertebral disc prosthesis, comprising: two plates; and a
cushion interposed between the plates, wherein the cushion
comprises a compressible chamber containing a compressible fluid
and extending around the periphery of the body and a distance from
the body.
20. Prosthesis according to claim 18 or 19, wherein the chamber
forms a spring.
21. Prosthesis according to claim 20, wherein the spring is a
compression spring.
Description
FIELD OF THE INVENTION
The invention relates to intervertebral disk prostheses.
European Patent No. 277 282-Al discloses an intervertebral disk
prosthesis, comprising two plates and a cushion interposed between
them. The cushion comprises a compressible body delimiting a cavity
filled with an incompressible fluid. This prosthesis is essentially
incompressible in the axial direction and allows only a relative
inclination of the plates. This behavior is different from that of
a healthy, natural intervertebral disk.
An object of the invention is to provide a disk prosthesis which
more closely imitates and approximates the mechanical properties of
a healthy, natural intervertebral disk.
SUMMARY OF THE INVENTION
With a view to achieving this object, according to the invention an
intervertebral disk prosthesis is envisaged comprising two plates
and a cushion interposed between the plates, the cushion comprising
a compressible body and containing a fluid, which is
compressible.
Thus the compression of the cushion affects the compression of the
body and the fluid. Since the compression properties of the body
and the fluid can be different, their combination allows a very
close approximation to the mechanical properties of a healthy,
natural intervertebral disk. More particularly, when the body is
made of suitable material, the curve of the mechanical reaction to
a compression of the cushion as a function of a variation in a
dimension of the cushion in the direction of compression can be
obtained, having a hysteresis shape close to that associated with a
healthy, natural disk.
Advantageously, the fluid has a pressure such that it is more
compressible than the body.
This difference can thus be utilized to approximate as closely as
possible the mechanical properties of the healthy, natural
disk.
Advantageously, the fluid comprises a gas.
Advantageously, the cushion is arranged such that a fluid pressure
is applied directly to the plates.
Advantageously, the fluid extends around the periphery of the
body.
Advantageously, the body comprises a viscoelastic material,
preferably silicone.
The aforementioned curve, thus has a highly pronounced hysteresis
shape can thus be obtained.
Advantageously, the body is in contact with the plates.
Advantageously, the body has at least one end having a contact zone
with one of the plates, the prosthesis being arranged such that the
contact zone has a surface area which increases whenever a
stressing of the plate in the direction of the body is
increased.
For the lowest compression values, the mechanical reaction of the
prosthesis upon the compression of the body thus varies very little
as a function of the dimensional change in the cushion in the
direction of compression. In other words, the aforementioned curve
is little inclined relative to the horizontal for low compression
values and little force is provided in the initial operation. This
property reproduces that of a healthy, natural disk.
Advantageously, the contact zone is defined by a face of the plate
and an end face of the body, one of the two faces, typically the
face of the body, being curved and convex and the other face being
flat.
Advantageously, the contact zone is defined by a face of the plate
and an end face of the body, the two faces being curved in at least
one common direction and being respectively concave and convex, the
concave face having at least one radius of curvature greater than a
corresponding radius of curvature of the convex face.
As a result of this configuration, the variations in mechanical
reaction, previously mentioned, can be effected. Moreover, when the
body is free to shift laterally relative to the plate, as will be
seen later, this configuration guarantees the relative centering of
the two faces. For example, after the two faces have been mutually
offset, these curvatures enable them to re-center
automatically.
Advantageously, the body has at least one end in contact with one
of the plates, this end being free to move relative to the plate in
a direction parallel to the plate.
Advantageously, the end is accommodated in a recess of the plate
and forms a lateral abutment for the body.
The lateral displacements of the body relative to the plates can
thus be limited, or even barred.
Advantageously, the cushion comprises a shell containing the fluid
and arranged such that it has a cross-sectional area parallel to
the plates which is essentially invariable when variation occurs in
a compression of the cushion between the plates.
Advantageously, the cushion comprises a chamber containing the
fluid and extending around the periphery of the body at a
distance.
The erosion of the body by the chamber in the course of its
movement and the dispersion of particles of the body are thus
prevented.
Advantageously, the chamber forms a spring, especially a
compression spring.
The chamber thus influences the reaction of the cushion whenever
this is compressed.
Advantageously, the cushion is arranged to exhibit a
hysteresis-shaped curve of mechanical reaction to a compression as
a function of a variation in a dimension of the cushion in the
direction of the compression.
Advantageously, the cushion is arranged such that the reaction to
the compression grows less markedly for relatively low reaction
values than for relatively high reaction values.
Advantageously, the cushion is arranged such that the reaction to
the compression diminishes more markedly for relatively high
reaction values than for relatively low reaction values.
Advantageously, the cushion is arranged such that the reaction to
the compression has higher values when it grows than when it
diminishes.
Advantageously, the prosthesis is intended for the lumbar region of
the spine.
Other characteristics and advantages of the invention are yet to
appear in the following description of the preferred embodiments,
given by way of non-limiting examples.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a prosthesis according to the
invention;
FIG. 2 is a axial section along the plane II--II of the prosthesis
of FIG. 1;
FIG. 3 is an enlarged scale view of a detail D of FIG. 2;
FIG. 4 is a curve indicating the compression force F applied by th
o plates to the cushion as a function of the variation in the
distance separating them;
FIG. 5 is a sectional view of a detail of an illustrative
embodiment of the prosthesis; and
FIG. 6 is a simplified view analogous to FIG. 2 showing a second
illustrative embodiment.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an intervertebral disk prosthesis 2 according to the
invention particularly intended for the lumbar region of the
vertebral column of the human body. The prosthesis 2 comprises two
flat plates 4 having the general shape of a bean with a posterior
hilum in plan view. Each plate 4 comprises a central circular panel
6 and a border 8 extending about the periphery of the panel 6 in
the plane thereof. At rest, the two plates 4 extend parallel to
each other, at a distance facing each other with their contours in
alignment. On each plate 4, the border 8 and the panel 6 each have
a groove 17 for the reception of a seal.
The disk prosthesis 2 comprises a cushion or intermediate part 10
interposed between the two plates 4. The cushion comprises a
compressible solid body 12, here made of viscoelastic material, for
example silicone. This body has a Shore-A hardness advantageously
60 to 100, in this case approximately 80. The body 12 has a shape
of revolution about its main axis 14. It has a cylindrical lateral
face 16 and two axial end faces 18 generally perpendicular to the
axis 14 and of slightly convex spherical shape. Each face 18 thus
has two identical curvatures in mutually perpendicular planes. The
body 12 is disposed coaxially with the panels 6. Each panel 6 has a
plane inner central face 20 perpendicular to the axis 14 and in
contact with one of the respective axial ends 18 of the body 12.
Thus, the convex spherical face 18 of the body rests on the plane
face 20 of the plate. The body 12 rests without anchorage on each
of the plates 4 such that it is movable relative to each of these
plates in a direction parallel to the plates, that is to say
perpendicular to the main axis 14. Given the compression of the
body 12 exerted by the plates 4, and the form of the faces of the
plates and the body, the mobility in this direction is manifested
by a rolling movement, optionally without sliding, of each axial
end 18 of the body on the face 20 of the plate with which it is in
contact. The body thus rolls between the two plates. The two plates
are thus laterally displaced relative to each other while remaining
parallel, if necessary. The transmission of lateral stresses from
the one to the other of the vertebrae is thus prevented.
The cushion 10 additionally comprises a bellows 22. The bellows
coaxially surrounds the body 14 at a distance therefrom. The
bellows 22 has a symmetrical shape in revolution about the axis 14.
Its wall profile comprises corrugations 24 allowing the length of
the bellows 22 to be varied in the axial direction 14 without any
appreciable variation in the surface area of its cross section
transverse to the axis 14. The bellows 22, like the plates 4, may
be made of titanium or titanium alloy, so that it has a certain
axial rigidity and forms a compression spring. The bellows can also
be deformed in a direction perpendicular to the axis 14 or can be
twisted about the axis 14 or about any axis perpendicular
thereto.
At its two axial ends, the bellows 22 has edges bonded to
respective edges of the panels 6 projecting from the inner face 20.
The bonding is leaktight so that the bellows 22 and the two panels
6 define a variable-volume, leaktight chamber extending around the
body 12. This chamber contains a fluid, for example a gas, such as
air. The undulations 24 nearest to the body 12 extend at a distance
from the latter to allow a free circulation of gas from the one to
the other of the dishes 6.
As shown, the bellows 22 has ten convolutions, with eight outer
crests in addition to two crests for securement to the plates. The
outer diameter is about 30 mm and the inner diameter is about 17
mm. Its height, when the prosthesis is not bonded, measures about
10 mm. The wall of the bellows can be produced by means of one, two
or three sheets, each measuring about 0.1 mm thick. The sum of the
thicknesses of the sheets forms the thickness of the wall. The
bellows here has an inherent strength of around 1.6 N/mm.
Each border 8 comprises two lugs 25 projecting from an outer face
of the plate 4 perpendicularly to the plane of the plate. Each lug
25 has an orifice 27 traversing through it in the direction of the
center of the plane and, a spherical recess directed away from the
plate 4 on one face of the lug 25. The orifices 27 are able to
receive a bone screw 26 having a head 28, whose lower face has a
male spherical shape cooperating with the female recess of the lug
25 to allow free orientation of the screw 26 relative to the
associated lug.
For short-term anchoring of the disc prosthesis 2 in the spine, the
screws 26 can be anchored in the spondylus of the vertebrae
adjacent to the disk to be replaced.
A "long term" anchorage might be envisaged, in which the surfaces
of the plates 4 in contact with the adjacent vertebrae are covered
with hydroxyapatite, or with any other substance known per se for
stimulating bone growth. Prior to being covered, the surfaces can
be treated to obtain a more or less porous surface condition, with
anchoring points for the bone tissue, in order to ensure a better
interface with the bone tissue.
FIG. 4 shows the path of the curve C, indicating the intensity of a
compression force F exerted on the cushion 10 (that is to say on
the two plates 4), disregarding their deformability, which is
virtually nil, in the axial direction 14, as a function of the
variation in length 1 of the cushion in the axial direction 14 (or
in the distance between the two plates). This curve also represents
the mechanical reaction R of the cushion 10 under the same
conditions.
This curve C is not linear. Moreover, it has a hysteresis form: the
curve Ca indicating the increase in the compression F from the zero
origin being distinct from the curve Cd indicating the decrease in
the compression F up to the origin, and extending entirely above
it. This pronounced hysteresis form is due principally to the
viscoelastic material of the body and secondarily to the
combination of the body 12 and the fluid in the cushion 10.
In addition, the curve Ca, relating to the increase in the
compression force F, exhibits a gently sloping portion Ca1 from the
origin O, then a more heavily sloping portion Ca2. The curve Cd
illustrating the decrease in the compression F exhibits for the
highest values of the force F a markedly sloping portion Cd1, then
for the lowest values of the force F a more gently sloping portion
Cd2. The presence of a gently sloping portion in the vicinity of
the origin for the curves Ca and Cd is due principally to the
configuration of the contact faces 18, 20 of the body 12 and of the
plates 4, the effect of which is to increase the surface area of
the mutual contact zone between each plate and the body, generally
in the form of a disk, whenever the force F is increased. This
increase occurs until the maximum surface area of the contact zone
is reached, when the whole of the face 18 is touching the plate
4.
The connecting points Ja and Jd respectively form the junction
between the curves Ca1 and Ca2 and Cd1 and Cd2. On the curve Ca,
the point Ja corresponds to the force F at which the maximum
contact surfaces between the plates and the body are reached.
Likewise, on the curve Cd, the point Jd corresponds to the force at
which these surfaces cease to be at a maximum.
The prosthesis can be configured such that the point Ja corresponds
to a value of .DELTA.l between 25% and 75% of the maximum variation
in length envisaged for the prosthesis during use.
Referring to FIG. 5, in an alternate embodiment, (otherwise having
the other characteristics of the prosthesis of FIG. 1) the face 20
of each plate 4 opposite the body 12 has a recess 32, in this case,
a U-shaped recess, forming a lateral abatement, in which the
corresponding axial end 18 of the body fits. The relative lateral
displacements of the body 12 with respect to each plate 4 are thus
limited to a certain range, or even totally barred.
In the alternate embodiment shown in FIG. 6, the face 20 can be
curved and concave in one or both directions, as shown, and the
face 18 can be curved and convex in the corresponding direction(s),
the radius of curvature of the face 20 being, for each direction,
greater than that of the face 18 in the corresponding direction.
The two faces 18, 20 are spherical as shown. The radii of curvature
of the surfaces 18 and 20 will, for example, be within the range of
about 70 to about 80 mm, and between about 140 to about 200 mm
respectively. Such an arrangement allows the two faces to be
centered automatically, while at the same time permitting a
relative lateral displacement of the body 12 relative to the plate
in any direction whatsoever perpendicular to a longitudinal
direction of the spine.
In the embodiment shown in FIG. 2, the two ends of the body 12 have
a contact surface 18 with the associated plate of variable surface
area, making it laterally movable relative to the body.
By contrast, in the alternate embodiment shown in FIG. 6, only one
of the ends 18 of the body 12 exhibits this property. The other
end, being the lower end in FIG. 6, has a plane circular shape with
an invariable contact zone with the associated plate and fixed
relative to the latter.
Of course, numerous modifications might be made to the invention
without departing from the scope thereof.
The fluid might be a liquid, or even a mixture of a liquid and a
gas, the latter being, for example, weakly soluble in the
liquid.
The body might have an elliptical shape in cross section to the
axis 14.
The inner face 20 of the plates 4 might be convex, the axial end
face 18 of the body 12 being flat, or concave with a greater radius
of curvature than that of the face 20 of the plate. The two
contacting faces of the plate and the body might be convex.
The curvature of the faces might be limited to a single plane.
The characteristics relating to the envelope 22 (spring effect,
distance to the body 12) might be effected independently of the
other characteristics.
Although the invention herein has been described with reference to
particular embodiments, it is to be understood that these
embodiments are merely illustrative of the principles and
applications of the present invention. It is therefore to be
understood that numerous modifications may be made to the
illustrative embodiments and that other arrangements may be devised
without departing from the spirit and scope of the present
invention as defined by the appended claims.
* * * * *